Influence of Topography and Winds on the Distribution of Water Masses on the Antarctic Continental Shelf

Abstract Central to improving our knowledge of ocean temperature change on Antarctica’s continental shelf is a better understanding of how ocean circulation drives the onshore flux of warm deep waters across the shelf break. This study uses a primitive equation ocean model to explore how the circulation regimes (throughflow and gyre—determined by basin geometry) and changes in surface stress influence the temperature structure on Antarctica’s shelf seas. Given the described shelf temperature changes are largely driven by ocean circulation changes, understanding these becomes our focus. A simple barotropic model is used to describe the linear theory of the difference between the circulation regimes and their expected responses to changes in forcing. This theory informs our understanding of the barotropic circulation response of the primitive equation model. A momentum and heat budget confirm, over simulated equilibrated time scales, that when the surface forcing changes, the response is first-order linear. Consistent with previous findings, we find that climate change projection-like wind shifts (stronger westerlies that shift south) directly influence Ekman processes across the shelf break and upwell warmer waters onto the shelf. We also find that the circulation regimes influence the mean shelf temperature and the susceptibility of existing shelf temperatures to surface stress change. In a throughflow regime, there can be a complete transition in on-shelf temperatures when the transition between westerly and easterly winds shifts southward. However, we find relatively modest warming at the coast in a gyre regime. Combinations of these regimes also experience coastal warming under a constant positive offset in winds. Significance Statement The Antarctic Slope Front determines how much warm water flows onto Antarctica’s continental shelf and the subsequent heat that is available to melt the ice shelves. This study explores the impact of basin geometry and wind shifts on the large-scale ocean circulation around the shelf with a focus on understanding changes in shelf temperature near an imagined ice front. Here, meridional topographic barriers change geometry, shedding insight into how different water temperatures on the shelf coalesce despite having the same initial conditions and wind forcing. Wind perturbation simulations suggest why some regions are more sensitive to shifts in winds than others. These findings highlight an underappreciated yet fundamentally important topographical constraint under future changes in winds.